Technical Field
[0001] The present invention relates to a liquid crystal display apparatus.
Background Art
[0002] A liquid crystal display apparatus has been utilized as display portions, such as
various meters and a navigation system arranged in the console of an automobile. Such
on-board liquid crystal display apparatus is mainly viewed by a driver, and hence
display characteristics (e.g., contrast and a tinge) at the four corners of a predetermined
region shifted upward with respect to a front direction (e.g., (viewing angle ϕ in
a vertical direction, viewing angle θ in a horizontal direction)=(+20°, +50°), (+20°,
-50°), (-20°, +50°), and (-20°, -50°)) are important. However, in a cpnventional liquid
crystal display apparatus, substantially only the control of viewing angle characteristics
symmetrical with respect to the front direction ((ϕ, θ)= (0°, 0°)) has been performed.
Therefore, a liquid crystal display apparatus improved in viewing angle characteristics
in a region vertically asymmetrical with respect to a front horizontal direction has
been desired.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0004] The present invention has been made to solve the above-mentioned conventional problem,
and an object of the present invention is to provide a liquid crystal display apparatus
improved in viewing angle characteristics in a region vertically asymmetrical with
respect to a front horizontal direction.
[0005] A liquid crystal display apparatus according to an embodiment of the present invention
includes: a liquid crystal cell including a liquid crystal layer containing liquid
crystal molecules aligned in homogeneous alignment under a state in which an electric
field is absent; a first polarizer arranged on a viewer side of the liquid crystal
cell; a second polarizer arranged on a back surface side of the liquid crystal cell;
a first optical compensation layer arranged between the liquid crystal cell and the
first polarizer; and a second optical compensation layer arranged between the liquid
crystal cell and the first optical compensation layer. A refractive index nz
1 in a thickness direction of the first optical compensation layer is less than 1.5187,
and a refractive index nz
2 in a thickness direction of the second optical compensation layer is less than 1.5340.
[0006] In one embodiment of the present invention, the first optical compensation layer
shows a refractive index characteristic of nx>ny>nz, and the second optical compensation
layer shows a refractive index characteristic of nz>nx>ny.
[0007] In one embodiment of the present invention, an initial alignment direction of the
liquid crystal cell and an absorption axis direction of the second polarizer are substantially
parallel to each other.
[0008] In one embodiment of the present invention, a slow axis direction of the first optical
compensation layer and a slow axis direction of the second optical compensation layer
are substantially parallel to each other.
[0009] In one embodiment of the present invention, the liquid crystal molecules of the liquid
crystal layer each have a pretilt.
[0010] In one embodiment of the present invention, an absorption axis direction of the first
polarizer is a horizontal direction of a viewer.
Advantageous Effects of Invention
[0011] According to the present invention, in the liquid crystal display apparatus including
the homogeneously aligned liquid crystal cell, the two optical compensation layers
are arranged on the viewer side of the liquid crystal cell, and the refractive index
in the thickness direction of each of the optical compensation layers is set to less
than a predetermined value, and hence the liquid crystal display apparatus improved
in viewing angle characteristics in the region vertically asymmetrical with respect
to the front horizontal direction can be obtained.
Brief Description of Drawings
[0012] FIG.
1 is a schematic sectional view of a liquid crystal display apparatus according to
one embodiment of the present invention.
Description of Embodiments
[0013] Embodiments of the present invention are described below with reference to the drawing.
However, the present invention is not limited to these embodiments.
(Definitions of Terms and Symbols)
[0014] The definitions of terms and symbols used herein are as described below.
(1) Refractive Indices (nx, ny, and nz)
[0015] "nx" represents a refractive index in a direction in which an in-plane refractive
index is maximum (that is, slow axis direction), "ny" represents a refractive index
in a direction perpendicular to the slow axis in the plane (that is, fast axis direction),
and "nz" represents a refractive index in a thickness direction.
(2) In-plane Retardation (Re)
[0016] "Re(λ)" refers to an in-plane retardation measured at 23°C with light having a wavelength
of λ nm. The Re(λ) is determined from the equation "Re= (nx-ny) ×d" when the thickness
of a layer (film) is represented by d (nm). For example, "Re(550)" refers to an in-plane
retardation measured at 23°C with light having a wavelength of 550 nm.
(3) Thickness Direction Retardation (Rth)
[0017] "Rth(λ)" refers to a thickness direction retardation measured at 23°C with light
having a wavelength of λ nm. The Rth(λ) is determined from the equation "Rth=(nx-nz)×d"
when the thickness of a layer (film) is represented by d (nm). For example, "Rth(550)"
refers to a thickness direction retardation measured at 23°C with light having a wavelength
of 550 nm.
(4) Nz Coefficient
[0018] An Nz coefficient is determined from the equation "Nz=Rth/Re".
(5) Substantially Perpendicular or Parallel
[0019] The expressions "substantially perpendicular" and "approximately perpendicular" include
a case in which an angle formed by two directions is 90°±10°, and the angle is preferably
90°±7°, more preferably 90°±5°. The expressions "substantially parallel" and "approximately
parallel" include a case in which an angle formed by two directions is 0°±10°, and
the angle is preferably 0°±7°, more preferably 0°±5°. Moreover, the simple expression
"perpendicular" or "parallel" as used herein may include a substantially perpendicular
state or a substantially parallel state.
(6) Subscript
[0020] The subscript "1" represents a first optical compensation layer, and the subscript
"2" represents a second optical compensation layer.
A. Overall Configuration of Liquid Crystal Display Apparatus
[0021] FIG.
1 is a schematic sectional view of a liquid crystal display apparatus according to
one embodiment of the present invention. A liquid crystal display apparatus
100 includes: a liquid crystal cell
10; a first polarizer
20 arranged on the viewer side of the liquid crystal cell
10; a second polarizer
30 arranged on the back surface side of the liquid crystal cell
10; a first optical compensation layer
40 arranged between the liquid crystal cell
10 and the first polarizer
20; and a second optical compensation layer
50 arranged between the liquid crystal cell
10 and the first optical compensation layer
40. The liquid crystal display apparatus
100 practically further includes a backlight unit. The backlight unit includes a light
source
60 and a light guide plate
70. The backlight unit may further include any appropriate other member (e.g., a diffusion
sheet or a prism sheet) . In the illustrated example, the backlight unit is of an
edge light system, but any appropriate other system (e.g., a direct system) may be
adopted for the backlight unit.
[0022] The first optical compensation layer
40 typically shows a refractive index characteristic of nx>ny>nz, and the second optical
compensation layer
50 typically shows a refractive index characteristic of nz>nx>ny. Further, in the present
invention, a refractive index nz
1 in the thickness direction of the first optical compensation layer
40 is less than 1.5187, and a refractive index nz
2 in the thickness direction of the second optical compensation layer
50 is less than 1.5340. When two optical compensation layers showing predetermined refractive
index characteristics are arranged in a predetermined positional relationship, and
refractive indices in the thickness directions of the two optical compensation layers
are set within such ranges, contrast at each of four corners in a region vertically
asymmetrical with respect to a front horizontal direction (e.g., (viewing angle ϕ
in a vertical direction, viewing angle θ in a horizontal direction) = (+20°, +50°),
(+20°, -50°), (-20°, +50°), and (-20°, -50°)) can be improved. In particular, contrast
at each of the upper two corners (e.g., (ϕ, θ)=(+20°, +50°) and (+20°, -50°)) that
has heretofore been difficult to improve can be significantly improved. One achievement
of the present invention is that viewing angle characteristics (in particular, the
viewing angle characteristics of contrast) in the region vertically asymmetrical with
respect to the front horizontal direction are improved as described above.
[0023] The liquid crystal display apparatus of the present invention has a contrast at,
for example, each of (ϕ, θ)=(+20°, +50°), (+20°, -50°), (-20°, +50°), and (-20°, -50°)
of preferably 100 or more, more preferably 150 or more, still more preferably 200
or more. In addition, the liquid crystal display apparatus of the present invention
has a contrast at, for example, each of (ϕ, θ)=(+20°, +40°), (+20°, -40°), (-20°,
+40°), and (-20°, -40°) of preferably 500 or more, more preferably 650 or more, still
more preferably 750 or more.
[0024] The liquid crystal display apparatus according to the embodiment of the present invention
may be in a so-called O mode or a so-called E mode. The term "liquid crystal panel
in the O mode" refers to a liquid crystal display panel in which the absorption axis
direction of the polarizer arranged on the light source side of the liquid crystal
cell is substantially parallel to the initial alignment direction of the liquid crystal
cell. The term "liquid crystal panel in the E mode" refers to a liquid crystal panel
in which the absorption axis direction of the polarizer arranged on the light source
side of the liquid crystal cell is substantially perpendicular to the initial alignment
direction of the liquid crystal cell. The term "initial alignment direction of the
liquid crystal cell" refers to such a direction that, under a state in which an electric
field is absent, the in-plane refractive index of the liquid crystal layer obtained
as a result of alignment of liquid crystal molecules contained in the liquid crystal
layer becomes maximum (i.e., a slow axis direction). The liquid crystal display apparatus
is preferably in the O mode.
[0025] In the liquid crystal display apparatus according to the embodiment of the present
invention, the absorption axis direction of the first polarizer
20 and the absorption axis direction of the second polarizer
30 are typically substantially perpendicular to each other. In addition, the absorption
axis direction of the first polarizer
20 and the slow axis direction of the first optical compensation layer
40 are typically substantially perpendicular to each other. The slow axis direction
of the first optical compensation layer
40 and the slow axis direction of the second optical compensation layer
50 are typically substantially parallel to each other.
[0026] In one embodiment, the absorption axis direction of the first polarizer
20 is the horizontal direction of a viewer. Therefore, in this embodiment, when the
horizontal direction is defined as 0°, an axial relationship among the respective
optical films and the respective members forming the liquid crystal display apparatus
is typically as follows: the angle of the absorption axis of the first polarizer is
0°, the angle of the slow axis of the first optical compensation layer is 90°, the
angle of the slow axis of the second optical compensation layer is 90°, the angle
of the initial alignment direction of the liquid crystal cell is 90°, and the angle
of the absorption axis of the second polarizer is 90°.
[0027] The liquid crystal display apparatus according to the embodiment of the present invention
may further include any appropriate other member. For example, any other optical compensation
layer (retardation film) may be further arranged. The optical characteristics, number,
combination, arrangement positions, and the like of the other optical compensation
layers may be appropriately selected in accordance with, for example, purposes and
desired optical characteristics. The configuration of a liquid crystal display apparatus
that is well known and commonly used in the art may be adopted as a matter that is
not described herein.
[0028] Each member and each optical film forming the liquid crystal display apparatus are
described below.
B. Liquid Crystal Cell
[0029] The liquid crystal cell
10 has a pair of substrates
11 and
11', and a liquid crystal layer
12 serving as a display medium interposed between the substrates. In a general configuration,
a color filter and a black matrix are arranged on one substrate, and a switching element
configured to control the electro-optical characteristics of liquid crystal, a scanning
line configured to apply a gate signal to the switching element and a signal line
configured to apply a source signal thereto, and a pixel electrode and a counter electrode
are arranged on the other substrate. An interval (cell gap) between the substrates
is controlled by a spacer or the like. For example, an alignment film formed of polyimide
may be arranged on the side of each of the substrates in contact with the liquid crystal
layer.
[0030] In one embodiment, the liquid crystal layer contains liquid crystal molecules aligned
in homogeneous alignment under a state in which an electric field is absent. The term
"liquid crystal molecules aligned in homogeneous alignment" refers to liquid crystal
molecules in the following state: as a result of an interaction between an alignment-treated
substrate and each of the liquid crystal molecules, the alignment vector of each of
the liquid crystal molecules is aligned in a parallel and uniform manner with respect
to the plane of the substrate. Such liquid crystal layer (as a result, the liquid
crystal cell) typically shows a three-dimensional refractive index of nx>ny=nz. The
"ny=nz" as used herein includes not only a case in which ny is completely equal to
nz, but also a case in which ny is substantially equal to nz. Typical examples of
a drive mode using the liquid crystal layer showing such three-dimensional refractive
index include an in-plane switching (IPS) mode and a fringe field switching (FFS)
mode. The above-mentioned IPSmode includes a super in-plane switching (S-IPS) mode
and an advanced super in-plane switching (AS-IPS) mode, each of which adopts a V-shaped
electrode, a zigzag electrode, or the like. In addition, the above-mentioned FFS mode
includes an advanced fringe field switching (A-FFS) mode and an ultra fringe field
switching (U-FFS) mode, each of which adopts a V-shaped electrode, a zigzag electrode,
or the like.
[0031] In one embodiment, the liquid crystal molecules of the liquid crystal layer each
have a pretilt. That is, the alignment vector of each of the liquid crystal molecules
is slightly tilted with respect to the plane of the substrate. A pretilt angle is
preferably from 0.1° to 1.0°, more preferably from 0.2° to 0.7°. The liquid crystal
display apparatus according to the embodiment of the present invention exhibits a
significant effect when the liquid crystal molecules of the liquid crystal layer each
have a pretilt. In particular, the apparatus has the following technical meaning:
optical design in accordance with the pretilt can be performed.
C. Polarizer
[0032] Any appropriate polarizer may be adopted as each of the first polarizer and the second
polarizer (hereinafter sometimes collectively simply referred to as "polarizers").
For example, a resin film forming the polarizer may be a single-layer resin film,
or may be a laminate of two or more layers.
[0033] Specific examples of the polarizer including a single-layer resin film include: a
polarizer obtained by subjecting a hydrophilic polymer film, such as a polyvinyl alcohol
(PVA) -based film, a partially formalized PVA-based film, or an ethylene-vinyl acetate
copolymer-based partially saponified film, to dyeing treatment with a dichroic substance,
such as iodine or a dichroic dye, and stretching treatment; and a polyene-based alignment
film, such as a dehydration-treated product of PVA or a dehydrochlorination-treated
product of polyvinyl chloride. A polarizer obtained by dyeing the PVA-based film with
iodine and uniaxially stretching the resultant is preferably used because the polarizer
is excellent in optical characteristics.
[0034] The dyeing with iodine is performed by, for example, immersing the PVA-based film
in an aqueous solution of iodine. The stretching ratio of the uniaxial stretching
is preferably from 3 times to 7 times. The stretching may be performed after the dyeing
treatment, or may be performed while the dyeing is performed. In addition, the dyeing
may be performed after the stretching has been performed. The PVA-based film is subjected
to swelling treatment, cross-linking treatment, washing treatment, drying treatment,
or the like as required. For example, when the PVA-based film is immersed in water
to be washed with water before the dyeing, contamination or an antiblocking agent
on the surface of the PVA-based film can be washed off. In addition, the PVA-based
film is swollen and hence dyeing unevenness or the like can be prevented.
[0035] The thickness of the polarizer is preferably from 1 µm to 80 µm, more preferably
from 10 µm to 50 µm, still more preferably from 15 µm to 40 µm, particularly preferably
from 20 µm to 30 µm. When the thickness of the polarizer falls within such range,
durability under high temperature and high humidity required for on-board applications
can be excellent.
[0036] The polarizer preferably shows absorption dichroism at any wavelength in the wavelength
range of from 380 nm to 780 nm. The single layer transmittance of the polarizer is
preferably from 42.0% to 46.0%, more preferably from 44.5% to 46.0%. The polarization
degree of the polarizer is preferably 97.0% or more, more preferably 99.0% or more,
still more preferably 99.9% or more.
[0037] A protective layer (not shown) may be arranged on at least one surface of each of
the first polarizer
20 and the second polarizer
30. That is, each of the first polarizer
20 and the second polarizer
30 may be incorporated as a polarizing plate into the liquid crystal display apparatus.
[0038] The protective layer is formed of any appropriate film that may be used as a protective
layer for a polarizer. A material serving as a main component of the film is specifically,
for example: a cellulose-based resin, such as triacetylcellulose (TAC); a transparent
resin, such as a polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based,
polyimide-based, polyether sulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based,
polyolefin-based, (meth)acrylic, or acetate-based transparent resin; or a thermosetting
resin or a UV-curable resin, such as a (meth) acrylic, urethane-based, (meth)acrylic
urethane-based, epoxy-based, or silicone-based thermosetting resin or UV-curable resin.
A further example thereof is a glassypolymer, such as a siloxane-basedpolymer. In
addition, a polymer film described in
JP 2001-343529 A (
WO 01/37007 A1) may be used. For example, a resin composition containing a thermoplastic resin having
a substituted or unsubstituted imide group on a side chain thereof, and a thermoplastic
resin having a substituted or unsubstituted phenyl group and a nitrile group on side
chains thereof may be used as the material for the film, and the composition is, for
example, a resin composition containing an alternating copolymer formed of isobutene
and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may
be, for example, an extrudate of the resin composition.
[0039] When the protective layer is arranged on the viewer side of the first polarizer
20, the protective layer may be subjected to surface treatment, such as hard coat treatment,
antireflection treatment, anti-sticking treatment, or antiglare treatment, as required.
[0040] The thickness of the protective layer is typically 5 mm or less, preferably 1 mm
or less, more preferably from 1 µm to 500 µm, still more preferably from 5 µm to 150
µm. When the surface treatment is performed, the thickness of the protective layer
is a thickness including the thickness of a surface treatment layer.
[0041] When the protective layer (hereinafter referred to as "inner protective layer") is
arranged on the liquid crystal cell side of the first polarizer
20 and/or the second polarizer
30, the inner protective layer is preferably optically isotropic. The phrase "be optically
isotropic" refers to having an in-plane retardation Re (550) of from 0 nm to 10 nm
and a thickness direction retardation Rth (550) of from -10 nm to +10 nm. The inner
protective layer may include any appropriate material as long as the inner protective
layer is optically isotropic. The material may be appropriately selected from, for
example, the materials described above for the protective layer.
[0042] The thickness of the inner protective layer is preferably from 5 µm to 200 µm, more
preferably from 10 µm to 100 µm, still more preferably from 15 µm to 95 µm.
D. First Optical Compensation Layer
[0043] As described above, the first optical compensation layer typically shows a refractive
index characteristic of nx>ny>nz. As described above, the refractive index nz
1 in the thickness direction of the first optical compensation layer is less than 1.5187,
preferably 1.5181 or less, more preferably 1.5175 or less. The lower limit of the
nz
1 is, for example, 1.5160. When the refractive index in the thickness direction of
the first optical compensation layer is set within such range, by virtue of a synergistic
effect with an effect exhibited by setting the nz
2 to be described later to less than a predetermined value, the viewing angle characteristics
of contrast in the region vertically asymmetrical with respect to the front horizontal
direction (in particular, at a predetermined position in an upper region with respect
to the front horizontal direction) can be improved.
[0044] The in-plane retardation Re (550) of the first optical compensation layer is preferably
from 80 nm to 135 nm, more preferably from 90 nm to 130 nm, still more preferably
from 95 nm to 110 nm. When the in-plane retardation falls within such range, the front
contrast of the liquid crystal display apparatus can also be improved.
[0045] The thickness direction retardation Rth(550) of the first optical compensation layer
is preferably from 110 nm to 160 nm, more preferably from 130 nm to 150 nm, still
more preferably from 135 nm to 140 nm. When the thickness direction retardation falls
within such range, contrast in an oblique direction of a liquid crystal panel having
a pretilt angle can be improved.
[0046] The Nz coefficient of the first optical compensation layer is preferably from 1.20
to 1.90, more preferably from 1.25 to 1.50, still more preferably from 1.28 to 1.40.
When the Nz coefficient falls within such range, the contrast in the oblique direction
of the liquid crystal panel having a pretilt angle can be improved.
[0047] In one embodiment, the first optical compensation layer may be formed by subjecting
a resin film to stretching treatment. Specifically, the first optical compensation
layer having the above-mentioned desired optical characteristics (e.g., a refractive
index characteristic and a refractive index in a thickness direction) may be obtained
by appropriately selecting, for example, the kind of a resin forming the resin film,
conditions for the stretching (e.g., a stretching temperature, a stretching ratio,
and a stretching direction), and a method for the stretching. Any appropriate resin
maybe adopted as the resin forming the resin film. Specific examples thereof include
a cycloolefin-based resin (e.g., a norbornene-based resin), a polycarbonate-based
resin, and a cellulose-based resin.
[0048] The norbornene-based resin is a resin polymerized by using a norbornene-based monomer
as a polymerization unit. Examples of the norbornene-based monomer include: norbornene,
alkyl and/or alkylidene substituted products thereof, such as 5-methyl-2-norbornene,
5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, and 5-ethylidene-2-norbornene,
and polar group (e.g., halogen) substituted products thereof; dicyclopentadiene and
2,3-dihydrodicyclopentadiene; dimethanooctahydronaphthalene, alkyl and/or alkylidene
substituted products thereof, and polar group (e.g., halogen) substituted products
thereof, such as 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthal ene,
6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthale ne, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaph
thalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthal ene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthale
ne, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtha lene, and 6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydr
onaphthalene; and trimers or tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene
and 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dod ecahydro-1H-cyclopentaanthracene.
The norbornene-based resin may be a copolymer of the norbornene-based monomer and
another monomer.
[0049] An aromatic polycarbonate is preferably used as the polycarbonate-based resin. The
aromatic polycarbonate may be typically obtained by a reaction between a carbonate
precursor and an aromatic dihydric phenol compound. Specific examples of the carbonate
precursor include phosgene, bischloroformates of dihydric phenols, diphenyl carbonate,
di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and dinaphthyl
carbonate. Of those, phosgene and diphenyl carbonate are preferred. Specific examples
of the aromatic dihydric phenol compound include 2,2-bis(4-hydroxyphenyl)propane,
2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,
2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane, 2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane,
1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
Those compounds may be used alone or in combination thereof. Of those, 2,2-bis(4-hydroxyphenyl)propane,
1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane
are preferably used. In particular, 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane
are preferably used in combination.
[0050] The cellulose-based resin is preferably a cellulose organic acid ester or a cellulose
mixed organic acid ester obtained by substituting part or all of the hydroxy groups
of cellulose with an acetyl group, a propionyl group, and/or a butyl group. Examples
of the cellulose organic acid ester include cellulose acetate, cellulose propionate,
and cellulose butyrate. Examples of the cellulose mixed organic acid ester include
cellulose acetate propionate and cellulose acetate butyrate. The cellulose-based resin
maybe obtained by, for example, a method described in paragraphs [0040] and [0041]
of
JP 2001-188128A. The acetyl substitution degree of the cellulose acetate is preferably from 2.0 to
3.0, more preferably from 2.5 to 3.0. The propionyl substitution degree of the cellulose
propionate is preferably from 2.0 to 3.0, more preferably from 2.5 to 3.0. In the
case where the cellulose-based resin is a mixed organic acid ester obtained by substituting
part of the hydroxy groups of cellulose with an acetyl group and substituting another
part thereof with a propionyl group, the total of its acetyl substitution degree and
propionyl substitution degree is preferably from 2.0 to 3.0, more preferably from
2.5 to 3.0. In this case, the acetyl substitution degree is preferably from 0.1 to
2.9, and the propionyl substitution degree is preferably from 0.1 to 2.9.
[0051] Examples of the stretching method include lateral uniaxial stretching, fixed-end
biaxial stretching, and sequential biaxial stretching. The stretching temperature
is preferably from 135°C to 165°C, more preferably from 140°C to 160°C. The stretching
ratio is preferably from 1.2 times to 3.2 times, more preferably from 1.3 times to
3.1 times.
[0052] When the first optical compensation layer is formed by stretching the resin film,
its thickness is preferably from 10 µm to 100 µm, more preferably from 20 µm to 80
µm, still more preferably from 30 µm to 60 µm.
[0053] In another embodiment, the first optical compensation layer may be formed from an
applied film of a non-liquid crystalline polymer. Specific examples of the non-liquid
crystalline polymer include polyamide, polyimide, polyester, polyetherketone, polyamide-imide,
and polyesterimide. Those polymers may be used alone or in combination thereof. Of
those, polyimide is particularly preferred because the polyimide has high transparency,
a high alignment property, and a high stretching property. In this embodiment, the
first optical compensation layer may be typically formed by applying a solution of
the non-liquid crystalline polymer to a substrate film and removing its solvent. In
the formation method, treatment (e.g., stretching treatment) for imparting optical
biaxiality (nx>ny>nz) is preferably performed. When such treatment is performed, a
difference in refractive index (nx>ny) can be reliably imparted to the inside of the
plane of the layer. The first optical compensation layer formed on a substrate film
may be typically transferred onto the polarizer. A specific example of the polyimide
and a specific example of the method of forming an optical compensation layer are
a polymer and a method of producing an optical compensation film described in
JP 2004-46065 A. In this case, the thickness of the first optical compensation layer is preferably
from 0.1 µm to 10 µm, more preferably from 0.1 µm to 8 µm, still more preferably from
0.1 µm to 5 µm.
E. Second Optical Compensation Layer
[0054] As described above, the second optical compensation layer typically shows a refractive
index characteristic of nz>nx>ny. As described above, the refractive index nz
2 in the thickness direction of the second optical compensation layer is less than
1.5340, preferably 1.5321 or less, more preferably 1.5307 or less. The lower limit
of the nz
2 is, for example, 1.5300. When the refractive index in the thickness direction of
the second optical compensation layer is set within such range, by virtue of a synergistic
effect with the effect exhibited by setting the nz
1 described above to less than a predetermined value, the viewing angle characteristics
of contrast in the region vertically asymmetrical with respect to the front horizontal
direction (in particular, at a predetermined position in an upper region with respect
to the front horizontal direction) can be improved.
[0055] The in-plane retardation Re (550) of the second optical compensation layer is preferably
from 25 nm to 55 nm, more preferably from 30 nm to 50 nm, still more preferably from
35 nm to 45 nm. When the in-plane retardation falls within such range, the front contrast
of the liquid crystal display apparatus can also be improved.
[0056] The thickness direction retardation Rth(550) of the second optical compensation layer
is preferably from -105 nm to -65 nm, more preferably from -100 nm to -75 nm, still
more preferably from -90 nm to -85 nm. When the thickness direction retardation falls
within such range, contrast in an oblique direction of a liquid crystal panel having
a pretilt angle can be improved.
[0057] The Nz coefficient of the second optical compensation layer is preferably from -4.2
to -1.5, more preferably from -3.0 to -2.1, still more preferably from -2.8 to -2.4.
When the Nz coefficient falls within such range, the contrast in the oblique direction
of the liquid crystal panel having a pretilt angle can be improved.
[0058] The second optical compensation layer typically includes a resin film. A material
for the resin film is typically, for example, a resin material having negative birefringence.
Specific examples of the resin material include an acrylic resin, a styrene-based
resin, a maleimide-based resin, and a fumarate-based resin.
[0059] The thickness of the second optical compensation layer is preferably from 5 µm to
50 µm, more preferably from 10 µm to 35 µm.
F. Backlight Unit
[0060] The light source
60 is arranged at a position corresponding to a side surface of the light guide plate
70. For example, a LED light source formed by arraying a plurality of LEDs may be used
as the light source. Any appropriate light guide plate may be used as the light guide
plate
70. For example, a light guide plate having a lens pattern formed on its back surface
side or a light guide plate having a prism shape or the like formed on its back surface
side and/or its viewer side is used, so that light from a lateral direction can be
deflected in its thickness direction. A light guide plate having prism shapes formed
on its back surface side and its viewer side is preferably used. In the light guide
plate, the ridge line directions of the prism shape formed on the back surface side
and the prism shape formed on the viewer side are preferably perpendicular to each
other. When such light guide plate is used, light that is more easily converged can
be caused to enter a prism sheet (not shown).
Industrial Applicability
[0061] The liquid crystal display apparatus of the present invention can be suitably used
for on-board devices, such as various meters arranged in a console, a reverse monitor,
a monitor for a car navigation system, and a car audio.
Reference Signs List
[0062]
- 10
- liquid crystal cell
- 20
- first polarizer
- 30
- second polarizer
- 40
- first optical compensation layer
- 50
- second optical compensation layer
- 100
- liquid crystal display apparatus